In an electronic system, components must be mounted on some interconnection network for communication to other parts of the system. The components of various types and configurations can be attached to a printed circuit board (PCB) to make the board a functional electronic device. To reduce costs of the assembly, semiautomatic or automatic insertion of components into PCBs are employed. However, multi-leaded components, e.g. integrated circuits, present problems for semiautomatic or automatic assembly because of lack of uniformity of body size and shape, difficulty of maintaining desired lead conditions, and feed problems at the input to insertion mechanisms. Successful mechanized assembly for integrated circuits is being achieved by using relatively standard integrated circuit (IC) packages. For example, dual in-line IC packages (DIP) that have two rows of vertical leads insertable into a PCB may be used for 256K dynamic RAMs.
For dynamic RAMs of 1M or more, zigzag in-line IC packages (ZIP) and single in-line IC packages (SIP) are used. Referring to FIGS. 1A and 1B respectively showing front and bottom views of a ZIP package, this type of IC package has two rows of leads L1-L20 arranged in a zigzag pattern along the bottom edge of the package.
As shown in FIG. 1C, the ZIP package may comprise a semiconductor chip 10 sealed by a sealing 12 made of epoxy resin. The leads L1-L20 may be connected to bonding pads of the chip 10 using gold wires. For example, a 1M.times.9 or 4 M.times.9 RAM may be incorporated into the chip 10. As shown in FIG. 2, a SIP package has a single row of leads aligned along the bottom edge.
Suitable packages for an integrated circuit must satisfy a series of requirements. They must be strong enough mechanically to withstand the stresses occurring during use and provide easily established and reliable electrical connection from the circuit inside to the outer world.
To provide an IC package assembly, for example, a memory module of very high capacity, a group of IC packages are usually assembled on a printed circuit (PC) carrier interconnected with a system PCB that carries the circuits to be connected with the inner circuits of the IC packages. FIG. 3 illustrates an example of a module having nine IC packages 20 mounted on a PC carrier 22 inserted into a system PCB 24. Soldering is used for attaching the IC packages to the PC carrier. However, the manufacturing of the PC-based assembly is a very demanding and expensive technological endeavor requiring sophisticated processes and machinery. In particular, the manufacturing sequence may incorporate the steps of solder paste application, solder paste baking out, reflow soldering, solvent cleaning and final inspection.
Moreover, a multi-package IC assembly based on a PC carrier has a high profile with respect to a system PCB. For some applications, for example, for laptop and notebook computers, and other portable systems, this is unacceptable because of size constraints.
Further, due to high packaging densities, heat generated within the packages can damage the packaged circuit. Metal heat sinks or other heat transfer means should be bonded to the PC carrier to absorb and disperse heat from operating IC packages. As a result, packaging density is reduced and manufacturing cost is increased.
Therefore, it would be desirable to provide a low-cost, high-density and low-profile IC package assembly that can replace a conventional PC-based assembly.